The present invention relates to gaming machines, in particular to gaming and slot machines such as poker machines, fruit machines, video gaming machines, video draw card poker machines and the like. In particular, the invention relates to an improved gaming machine wherein the probability of winning combinations occuring may be altered with regard to conventional machines without changing the number of actual symbols or indicia available e.g. the predetermined number of symbols which are available on a rotatable reel or reel-type gaming machine, or alternatively, that the number of physical symbols or indicia may be decreased, with a consequential increase in symbol size where the symbols are mounted on a reel, without altering the probability of winning combinations provided on the machine occurring.
The invention particularly, but not exclusively, relates to slot machines common to casinos and clubs where the player inserts coins into the machine and spins at least one rotatable reel by handle or button whereupon the reel or reels become stopped at random, and if the stop symbols coincide with the pay schedule or score card the player is paid a prize. If it is a multi-coin machine the player may buy extra chances or multiply potential winnings.
In a preferred embodiment the present invention applies to slot machines with reels, the stopping position of which is random but under the control of a microprocessor; machines of this type are described in British patent No. 1550732 by PBR and U.S. Pat. No. 4,095,795 by Saxton.
In a bid to attract players, casinos have offered higher and higher jackpots, and as these are a percentage of revenue the chances of striking a jackpot have to be proportionally less. This was attained in the past, in reel machines, by increasing the number of reels and increasing the number of symbols on a reel.
With the development of microprocessor control gaming machines, where the stopping position of the reel is determined by the microprocessor, a new approach was taken. Telnaes U.S. Pat. No. 4,448,419 selected stopping positions from a virtual reel strip or memory table within the microprocessor which had more virtual positions than there were physical stop positions on the reel itself. By mapping several of these virtual positions to one of the reel symbols, the probability of the reel showing one symbol became different to that for showing others of the symbols. For example, a jackpot symbol can be made to appear with less frequency than other symbols.
With the same intention, U.S. Pat. No. 4,858,932 to Keane selects the reel stopping position from a series of random numbers divided into the same number of groups as there are reel positions; however the size of each group is unequal, thereby causing the appearance of a jackpot or other symbol to be of unequal probability of appearing on a pay line.
Kabushiki Kaisha Universal also describe an arrangement in their Australian patent No. 561873 in which the slot machine periodically checks the prize value paid by the machine over the preceding period, and if this value is too high the machine adjusts the operation of the machine to make it harder for the player to win. The Kabushiki Kaisha Universal machine is of the type where the reels are stopped under player control by the player pressing a stop button and winning is made harder by introducing a delay in the reel stopping sequence after the stop button is pressed. British patent No. 2201279 (Chadwick) and U.S. Pat. Nos. 4,711,451 (Pajak) and 4,467,143 (Hagiwara) also describe methods of reducing the pay out rates of slot machines, but generally by changing the pay out for a given result rather than by changing the probability of the result occurring.
The present invention provides a gaming machine comprising display means arranged to display at least one indicium selected from a set of a plurality of possible indicia, random selection means arranged to select the indicia to be displayed on said display means from said set of indicia, the random selection means including random number generation means arranged to select a random number from a set of numbers having a member uniquely corresponding to each indicium of the set of possible indicia, wherein the set of numbers are divided between a plurality of subset tables, at least one of the subset tables containing a plurality of members, and selection means arranged to select between the subset tables to select a subset table as the table to be used for a current game on the machine, whereby the random number generator makes its selection from the selected table and the display means is responsive to the selected number to display the corresponding indicium.
The selection means is preferably arranged to make a weighted selection between the subset tables. In this way, one of the tables can include a number corresponding to a jackpot symbol or indicium and the selection can be weighted towards the table which does not include the jackpot symbol or indicium, thus allowing one to increase the value of the jackpot without needing to increase the number of symbols or indicia available.
At least two of the subset tables may contain an unequal number of members to each other. For example, where there are two subset tables only, one could contain 17 numbers and the other could contain 3 numbers, one of the three numbers being a jackpot symbol.
The present invention further provides a method of operating a gaming machine, having display means arranged to display at least one indicia selected from a set of a plurality of possible indicia, the machine being provided with a plurality of numbers representing indicia displayable by the display means, each displayable indicium being represented by a corresponding respective number, the plurality of numbers being divided into a plurality of subset tables, at least one of the subset tables having a plurality of members, the method of operation comprising selecting an indicium for display by the steps of randomly selecting one of the subset tables, randomly selecting one number from the subset table and displaying the indicium corresponding to the selected number.
The present invention yet further provides a gaming machine comprising control means for controlling operation of the machine, display means including a plurality of display positions for displaying combinations of indicia and reward means for returning a reward to a player of the machine in response to certain predetermined indicia combinations being displayed on the display means at the end of the game, the display means including a plurality of reels mounting the indicia, random selection means arranged to select the indicia to be displayed by at least one of the reels from a set of a plurality of possible indicia for the at least one reel, the random selection means including random number generation means arranged to select a random number from a set of numbers having a member uniquely corresponding to each indicium of the set of possible indicia, wherein the set of numbers are divided between a plurality of subset tables, at least one of the subset tables containing a plurality of members, and selection means arranged to select between the subset tables to select a subset table as the table to be used for a current game on the machine, whereby the random number generator makes its selection from the selected table and the reel is responsive to the selected number to display the corresponding indicium.